The present invention relates to an original reading apparatus provided in an image forming apparatus such as a copier or facsimile, and particularly to an automatic document feeding apparatus or feeder in an original reading apparatus.
In an optical reading apparatus provided in an image forming apparatus, methods of reading an original include a stationary original reading method in which transport means such as a belt or roller feeds an original on a platen, and an optical reading system scans the original placed stationary on the platen to read an image on the original, and a sheet through reading method in which an optical reading system situated at a fixed reading position reads an original while a feeding apparatus is transporting the original.
In the sheet through reading method, a conventional original reading apparatus includes the first platen for placing the original and the second platen arranged adjacent to the first platen. In the original reading apparatus, reading means moves in a sub-scanning direction (original transport direction) to read the original such as a book placed stationary on the first platen. Also, the original supplied from a sheet supply tray in an original feeding apparatus passes over the second platen, and the stationary reading means established below the second platen reads an image on the original.
In the conventional original reading apparatus with a configuration described above, as shown in FIG. 6(a), a reading unit is provided with a pair of feed rollers 102 arranged upstream of the second platen 101, a pair of discharge rollers 103 arranged downstream of the second platen 101, and an curved reading path 106 including a guide 104 facing an upper surface of the second platen 101. After the feed rollers 102 feed the original from a sheet supply tray (not shown) disposed upstream of the feed rollers 102 to the second platen 101, a lifting member 105 disposed between the first platen 100 and the second platen 101 lifts and guides the original from the upper surface of the second platen 101 to the discharge rollers 103.
However, in the reading unit of such an original reading apparatus, when the lifting member 105 lifts a leading edge of the original from the second platen 101, the leading edge of the original strikes an oblique surface of the lifting member 105 to create a shock. As a result, the original tends to vibrate or be transported at a various speed at the reading position, thereby causing distortion of the read image. Further, when a trailing edge of the original passes through and exits a nipping point of the feed rollers 102, the trailing edge of the original drops downward to cause an unsteady transport of the original and a variation in the speed of the original, thereby causing distortion of the read image.
To solve these problems, another conventional apparatus is provided with a transparent film member 207 on the second platen 201, as shown in FIG. 6(b), so that the original is transported along the transparent film member 207.
The transparent film member 207 is arranged between a guide 204 and the second platen 201, and forms a curved reading path between the guide 204 and the film member 207. An end 207a of the transparent film member 207 is fastened to a backside of the guide 208 at an upstream side of the reading path 206, and the other end 207b is free and inserted into an inside of a downstream guide 209 of the reading path 206.
The transparent film member is made of a flexible material such as polyethylene terephthalate (Mylar), and is positioned to face substantially the entire length of the second platen 201 and touch the upper surface of the second platen 201. With this configuration, the feed rollers 202 feed the original supplied to the reading unit between the transparent film member 207 and the guide 204 to pass above the second platen 201. The reading means located stationary below the second platen 201 at the reading position reads the image on the original through the second platen 201 and the transparent film member 207. After reading the image, the original is guided to the discharge rollers 203 along the transparent film member 207 to discharge.
In the conventional automatic document feeder with the configuration described above, when the transparent film member 207 lifts the original, the leading edge of the original does not strike anything, thereby making it possible to obtain a good quality image. However, there is still a problem in which when the original passes through the nipping point of the feed rollers, the trailing edge of the original drops. Therefore, the original vibrates while transporting at various speeds at the reading position, thereby making it difficult to obtain a good quality image from the original.
In view of the problems describe above, an object of the present invention is to provide an automatic document feeder in which the original can be transported smoothly from the leading edge to the trailing edge at the reading position with a simple structure to obtain a good quality image.
Further objects and advantages of the invention will be apparent from the following description of the invention.